Abstract
Nearby active stars with relatively rapid rotation and large starspot structures offer the opportunity to compare interferometric, spectroscopic, and photometric imaging techniques. In this ...paper, we image a spotted star with three different methods for the first time. The giant primary star of the RS Canum Venaticorum binary
σ
Geminorum (
σ
Gem) was imaged for two epochs of interferometric, high-resolution spectroscopic, and photometric observations. The light curves from the reconstructions show good agreement with the observed light curves, supported by the longitudinally consistent spot features on the different maps. However, there is strong disagreement in the spot latitudes across the methods.
Based on CHARA Array measurements, we present the angular diameters of 23 nearby, main-sequence stars, ranging from spectral types A7 to K0, 5 of which are exoplanet host stars. We derive linear ...radii, effective temperatures, and absolute luminosities of the stars using Hipparcos parallaxes and measured bolometric fluxes. The new data are combined with previously published values to create an Angular Diameter Anthology of measured angular diameters to main-sequence stars (luminosity classes V and IV). This compilation consists of 125 stars with diameter uncertainties of less than 5%, ranging in spectral types from A to M. The large quantity of empirical data is used to derive color-temperature relations to an assortment of color indices in the Johnson (BVR sub(J)I sub(J)JHK), Cousins (R sub(C)I sub(C)), Kron (R sub(K)I sub(K)), Sloan (griz), and WISE (W sub(3)W sub(4)) photometric systems. These relations have an average standard deviation of ~3% and are valid for stars with spectral types A0-M4. To derive even more accurate relations for Sun-like stars, we also determined these temperature relations omitting early-type stars (T sub(eff) > 6750 K) that may have biased luminosity estimates because of rapid rotation; for this subset the dispersion is only ~2.5%. We find effective temperatures in agreement within a couple of percent for the interferometrically characterized sample of main-sequence stars compared to those derived via the infrared flux method and spectroscopic analysis.
The physical processes occurring within the inner few astronomical units of protoplanetary disks surrounding Herbig Ae stars are crucial to setting the environment in which the outer planet-forming ...disk evolves and put critical constraints on the processes of accretion and planet migration. We present the most complete published sample of high angular resolution H- and K-band observations of the stars HD 163296 and HD 190073, including 30 previously unpublished nights of observations of the former and 45 nights of the latter with the CHARA long-baseline interferometer, in addition to archival VLTI data. We confirm previous observations suggesting that significant near-infrared emission originates within the putative dust evaporation front of HD 163296 and show that this is the case for HD 190073 as well. The H- and K-band sizes are the same within (3 3)% for HD 163296 and within (6 10)% for HD 190073. The radial surface brightness profiles for both disks are remarkably Gaussian-like with little or no sign of the sharp edge expected for a dust evaporation front. Coupled with spectral energy distribution analysis, our direct measurements of the stellar flux component at the H and K bands suggest that HD 190073 is much younger (<400 kyr) and more massive (∼5.6 M ) than previously thought, mainly as a consequence of the new Gaia distance (891 pc).
The bright star 55 Cancri is known to host five planets, including a transiting super-Earth. The study presented here yields directly determined values for 55 Cnc's stellar astrophysical parameters ...based on improved interferometry: R = 0.943 ? 0.010 R , T EFF = 5196 ? 24 K. We use isochrone fitting to determine 55 Cnc's age to be 10.2 ? 2.5 Gyr, implying a stellar mass of 0.905 ? 0.015 M . Our analysis of the location and extent of the system's habitable zone (HZ; 0.67-1.32 AU) shows that planet f, with period ~260 days and Msin i = 0.155 M Jupiter, spends the majority of the duration of its elliptical orbit in the circumstellar HZ. Though planet f is too massive to harbor liquid water on any planetary surface, we elaborate on the potential of alternative low-mass objects in planet f's vicinity: a large moon and a low-mass planet on a dynamically stable orbit within the HZ. Finally, our direct value for 55 Cancri's stellar radius allows for a model-independent calculation of the physical diameter of the transiting super-Earth 55 Cnc e (~2.05 ? 0.15 R {circled plus}), which, depending on the planetary mass assumed, implies a bulk density of 0.76 Delta *r{circled plus} or 1.07 Delta *r{circled plus}.
We present direct radii measurements of the well-known transiting exoplanet host stars HD 189733 and HD 209458 using the CHARA Array interferometer. We find the limb-darkened angular diameters to be ...θLD = 0.3848 ± 0.0055 and 0.2254 ± 0.0072 mas for HD 189733 and HD 209458, respectively. HD 189733 and HD 209458 are currently the only two transiting exoplanet systems where detection of the respective planetary companion's orbital motion from high-resolution spectroscopy has revealed absolute masses for both star and planet. We use our new measurements together with the orbital information from radial velocity and photometric time series data, Hipparcos distances, and newly measured bolometric fluxes to determine the stellar effective temperatures (T
eff = 4875 ± 43, 6092 ± 103 K), stellar linear radii (R
* = 0.805 ± 0.016, 1.203 ± 0.061 R⊙), mean stellar densities (ρ* = 1.62 ± 0.11, 0.58 ± 0.14 ρ⊙), planetary radii (R
p = 1.216 ± 0.024, 1.451 ± 0.074 R
Jup), and mean planetary densities (ρp = 0.605 ± 0.029, 0.196 ± 0.033 ρJup) for HD 189733b and HD 209458b, respectively. The stellar parameters for HD 209458, an F9 dwarf, are consistent with indirect estimates derived from spectroscopic and evolutionary modelling. However, we find that models are unable to reproduce the observational results for the K2 dwarf, HD 189733. We show that, for stellar evolutionary models to match the observed stellar properties of HD 189733, adjustments lowering the solar-calibrated mixing-length parameter to αMLT =1.34 need to be employed.
We have executed a survey of nearby, main-sequence A-, F-, and G-type stars with the CHARA Array, successfully measuring the angular diameters of forty-four stars with an average precision of ~1.5%. ...We present new measures of the bolometric flux, which in turn leads to an empirical determination of the effective temperature for the stars observed. In addition, these CHARA-determined temperatures, radii, and luminosities are fit to Yonsei-Yale model isochrones to constrain the masses and ages of the stars. These results are compared to indirect estimates of these quantities obtained by collecting photometry of the stars and applying them to model atmospheres and evolutionary isochrones. We find that for most cases, the models overestimate the effective temperature by ~1.5%-4% when compared to our directly measured values. The overestimated temperatures and underestimated radii in these works appear to cause an additional offset in the star's surface gravity measurements, which consequently yield higher masses and younger ages, in particular for stars with masses greater than ~1.3 M sub(middot in circle). Additionally, we compare our measurements to a large sample of eclipsing binary stars, and excellent agreement is seen within both data sets. Finally, we present temperature relations with respect to (B - V) and (V - K) colors as well as spectral type, showing that calibration of effective temperatures with errors ~1% is now possible from interferometric angular diameters of stars.
Abstract
We present
H
-band interferometric observations of the red supergiant (RSG) AZ Cyg that were made with the Michigan Infra-Red Combiner (MIRC) at the six-telescope Center for High Angular ...Resolution Astronomy (CHARA) Array. The observations span 5 yr (2011–2016), which offers insight into the short and long-term evolution of surface features on RSGs. Using a spectrum of AZ Cyg obtained with SpeX on the NASA InfraRed Telescope Facility (IRTF) and synthetic spectra calculated from spherical MARCS, spherical PHOENIX, and SAtlas model atmospheres, we derive
T
eff
is between 3972 K and 4000 K and
log
g
between −0.50 and 0.00, depending on the stellar model used. Using fits to the squared visibility and GAIA parallaxes, we measure its average radius
R
=
911
−
50
+
57
R
⊙
. Reconstructions of the stellar surface using our model-independent imaging codes SQUEEZE and OITOOLS.jl show a complex surface with small bright features that appear to vary on a timescale of less than one year and larger features that persist for more than one year. The 1D power spectra of these images suggest a characteristic size of 0.52–0.69
R
⋆
for the larger, long lived features. This is close to the values of 0.51–0.53
R
⋆
that are derived from 3D RHD models of stellar surfaces. We conclude that interferometric imaging of this star is in line with predictions of 3D RHD models but that short-term imaging is needed to more stringently test predictions of convection in RSGs.
We use near-infrared interferometric data coupled with trigonometric parallax values and spectral energy distribution fitting to directly determine stellar radii, effective temperatures and ...luminosities for the exoplanet host stars 61 Vir, ρ CrB, GJ 176, GJ 614, GJ 649, GJ 876, HD 1461, HD 7924, HD 33564, HD 107383 and HD 210702. Three of these targets are M dwarfs. Statistical uncertainties in the stellar radii and effective temperatures range from 0.5 to 5 per cent and from 0.2 to 2 per cent, respectively. For eight of these targets, this work presents the first directly determined values of radius and temperature; for the other three, we provide updates to their properties. The stellar fundamental parameters are used to estimate stellar mass and calculate the location and extent of each system's circumstellar habitable zone. Two of these systems have planets that spend at least parts of their respective orbits in the system habitable zone: two of GJ 876's four planets and the planet that orbits HD 33564. We find that our value for GJ 876's stellar radius is more than 20 per cent larger than previous estimates and frequently used values in the astronomical literature.
We present models of the inner region of the circumstellar disk of RY Tau that aim to explain our near-infrared (K-band: 2.1 m) interferometric observations, while remaining consistent with the ...optical to near-infrared portions of the spectral energy distribution. Our submilliarcsecond-resolution CHARA Array observations are supplemented with shorter baseline, archival data from PTI, KI, and VLTI/GRAVITY and modeled using an axisymmetric Monte Carlo radiative transfer code. The K-band visibilities are well fit by models incorporating a central star illuminating a disk with an inner edge shaped by dust sublimation at 0.210 0.005 au, assuming a viewing geometry adopted from millimeter interferometry (65° inclined with a disk major axis position angle of 23°). This sublimation radius is consistent with that expected of silicate grains with a maximum size of 0.36-0.40 m contributing to the opacity, and is an order of magnitude further from the star than the theoretical magnetospheric truncation radius. The visibilities on the longest baselines probed by CHARA indicate that we lack a clear line of sight to the stellar photosphere. Instead, our analysis shows that the central star is occulted by the disk surface layers close to the sublimation rim. While we do not see direct evidence of temporal variability in our multiepoch CHARA observations, we suggest the aperiodic photometric variability of RY Tau is likely related temporal and/or azimuthal variations in the structure of the disk surface layers.
Abstract
Time series of spectroscopic, speckle-interferometric, and optical long-baseline-interferometric observations confirm that
ν
Gem is a hierarchical triple system. It consists of an inner ...binary composed of two B-type stars and an outer classical Be star. Several photospheric spectral lines of the inner components were disentangled, revealing two stars with very different rotational broadening (∼260 and ∼140 km s
−1
, respectively), while the photospheric lines of the Be star remain undetected. From the combined spectroscopic and astrometric orbital solution it is not possible to unambiguously cross identify the inner astrometric components with the spectroscopic components. In the preferred solution based on modeling of the disentangled line profiles, the inner binary is composed of two stars with nearly identical masses of 3.3
M
⊙
and the more rapidly rotating star is the fainter one. These two stars are in a marginally elliptical orbit (
e
= 0.06) about each other with a period of 53.8 days. The third star also has a mass of 3.3
M
⊙
and follows a more eccentric (
e
= 0.24) orbit with a period of 19.1 yr. The two orbits are codirectional, and at inclinations of 79° and 76° of the inner and the outer orbit, respectively, about coplanar. No astrometric or spectroscopic evidence could be found that the Be star itself is double. The system appears dynamically stable and not subject to eccentric Lidov–Kozai oscillations. After disentangling, the spectra of the components of the inner binary do not exhibit peculiarities that would be indicative of past interactions. Motivations for a wide range of follow-up studies are suggested.
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